Seat backs

ABSTRACT

The core ( 1 ) of a seat back, which will be upholstered to form the complete back, is a moulded plastics sheet bowed forwardly and with attachment points ( 12 ) near top and bottom for securing to a rigid support. The sheet is constructed to be stiffer over its upper portion then over the lower and, when secured, to be able to ripple or alter its curvature between the attachment points. It may have wings ( 2 ) inclining forwardly at each side with closed end slots ( 3 ) between the wings ( 2 ) and the central zone ( 8 ) of the core. The wings can be divided into generally horizontal sections carried by integrally moulded transverse ribs ( 4 ) spanning the slots ( 3 ), the division between sections being by slots ( 13 ) or narrow membranes ( 6 ). The top of the core may also be divided into side-by-sections, the division being by slots ( 14 ) or narrow membranes ( 11 ).

[0001] This invention relates to seat backs, and in particular to thecore which generally defines its shape and characteristics. This corewill generally be upholstered or sheathed in some way, but how the seatback supports the user and responds to his movements is dictated by thecore.

[0002] Between the extremes of a rigid seat back and a fully upholsteredone with internal springs, there are backs with a basic shape againstwhich a user's back will fit comfortably but which will flex to acertain extent when the user moves, in effect trying to accommodate to adifferent posture. They will also change shape a bit between users ofdifferent physique.

[0003] One particular characteristic is the forward bow of the centralpart of the seat back, which gives support to the user's lumbar region.It has been recognised that it is desirable for the shape of this bowedpart to be adjustable and there have been various proposals for alteringthis shape by some control mechanism. That is, the user can turn a knob,press a switch, or otherwise initiate some mechanical action that willpull or push the seat back into a different configuration. These maywell work quite satisfactorily, but they make for complexity andtherefore extra cost, and the user's control, if reasonably accessible,can spoil the otherwise “clean” lines of the seat.

[0004] It is the aim of this invention for the core of a seat back to beso constructed that it will accommodate well to different users and todifferent positions of users, while maintaining comfortable support,without extraneous control devices.

[0005] According to the present invention a seat back core comprises amoulded plastics sheet bowed forwardly in vertical section and withfixing points on the rear side near top and bottom for attachment to arigid seat member, the back being more resistant to bending over itsupper part than its lower part.

[0006] In the preferred form the sheet has side wings inclined forwardlyfrom narrow zones of weakness within the boundary of the sheet,symmetrically disposed either side of a vertical centre line andgenerally parallel thereto. These zones of weakness are convenientlyformed by closed end slots, and the wings and the central portion of thecore between the slots will generally be connected by bridges across theslots. Advantageously, these bridges are parts of transverse ribsintegrally moulded on the rear side of the sheet.

[0007] For further comfort the wings may be divided into generallyhorizontal sections each capable of limited flexure with respect to theor each adjacent section. The division between wing sections ispreferably by slots extending from the edge of the sheet to the adjacentzone of weakness, although it may be by expandable membranes integrallymoulded with the sheet and extending from the edge of the sheet to theadjacent zone of weakness.

[0008] The top edge portion of the core, beyond the zones of weakness,may also be divided into side-by-side sections each capable of limitedflexure with respect to the or each adjacent section. And as with thewing sections the division between top edge portion sections ispreferably by generally vertical slots extending down from the top edgeof the core although it may be by generally vertical, narrow, integrallymoulded expandable membranes.

[0009] The differential resistance to bending may be caused by furtherribs extending substantially vertically between transverse ribs in theupper part of said central zone. Alternatively, it may be caused bylocally reducing the thickness of the sheet by transverse grooves and/orscored lines across the lower part of the said central zone.

[0010] For a better understanding of the invention some embodiments willnow be described, by way of example, to the accompanying drawings, inwhich:

[0011]FIG. 1 is a front view of a backrest for a seat.

[0012]FIG. 2 is a rear view of the backrest of FIG. 1

[0013]FIG. 3 is a perspective view showing the rear of the backrest,

[0014]FIG. 4 is a sectional detail,

[0015]FIG. 5 is a rear view of another backrest

[0016]FIG. 6 is a perspective view showing the rear of the backrest ofFIG. 5, and

[0017]FIG. 7 is a section on the line VII-VII of FIG. 5.

[0018] The backrest 1 of FIGS. 1 to 4 is of moulded plastics such asnylon and has the general shape of a is shield bowed forwards invertical section and with side wings 2 curving further forwards. Thereare two closed end slots 3 extending vertically and symmetrically, oneat either side of the vertical centre line and stopping well short ofthe top and bottom edges of the shield. There could be thin membranesinstead of the slots 3, making narrow zones of weakness, but for ease ofmanufacture slots are preferred.

[0019] Integrally moulded reinforcing ribs 4 extend horizontally acrossthe backrest spanning the slots 3, and in doing so they form bridges 5.They do not start until about one third of the way up the shield, wherethey are clustered closer together than towards the top. Outside theslots 3 in the wings 2 of the shield there are horizontal webs orelongate membranes 6 alternating with the ribs 4. They are created bythinning and/or corrugating the material on both sides, an example ofwhich is shown in the section of FIG. 4. There are also webs 7 in thecentral zone 8 between the slots 3, these being created by horizontalgrooves in the front side only. They are not continuous, and they arealigned with only some webs 6 in the wings 2. Between them, over part ofthe central zone 8, there are lines 9 scored parallel to the webs 7 inthe sheet material which give a bit of extra flexibility.

[0020] Beyond the upper ends of the slots 3 there is anotherintermittent web 10, visible on both sides of the shield, and above thatthree webs or elongate corrugated membranes 11 extending down from theupper edge of the shield, one central and slightly longer than the twoothers, which are just inward of the slots 3.

[0021] On the rear face of the shield in the central zone 8 between theslots 3 there are four fixing points 12 where the shield is attached toa rigid support. Their arrangement is symmetrical with respect to thevertical centre line, with one pair near the top of the zone 8 and theother pair near the bottom of that zone, the points of each pair beingquite close together so that the backrest can be secured to a singlesupporting spine or narrow frame upstanding from the rear of the seat.While these attachment points are fixed, the rest of the shield can moveslightly under the constraints imposed by the stiffness of the materialand the ribs and the amount of freedom allowed by the webs. But inparticular, there is a capacity to “ripple” or alter its curvature fromtop to bottom or vice versa.

[0022] This construction is not easy to manufacture, the webs inparticular being tricky. The embodiment of FIGS. 5 to 7 may therefore bepreferred in practice.

[0023] Equivalent parts are similarly referenced. Much of the differencelies in having slots 13 and 14 instead of the webs 6 and 11 and inomitting the webs 7 and scored lines 9. The function of the latter wasto give greater flexibility to the lower part of the central section 8,the upper part remaining relatively stiff. While the lower part shouldripple quite easily, the upper part should have more limited capacity todeform. To maintain these different characteristics between the upperand lower parts, the material of the upper part could be thicker thanthat of the lower part, but preferably, as shown in FIGS. 5, 6 and 7, atleast some of the ribs 4 spanning the upper part are joined by furthervertical ribs 15 symmetrical with respect to the vertical centre line.It will be understood that the number, size and distribution of theseribs can vary from what is shown, to tailor the flexibility of the corewith some precision.

[0024] Two ribs 15 a extend between the two uppermost ribs 4 andincorporate the upper fixing points 12, which are also incorporated in ashort transverse rib 16. This reinforces the core in the upper zone ofattachment and there is similar reinforcement in the lower zone. Thathas a very short vertical extent and it does not affect the ability ofthe core to ripple above the second lowermost transverse rib 4.

[0025] The slots 3 are shown as straight and parallel. This may bevaried, for example by having them slightly divergent or curved.

[0026] Provision may be made for setting up the backrest with adifferent curvature. For example, there could be an extra pair of fixingpoints immediately below the lower pair, and by attaching the spine tothis extra pair the forward bow of the zone 8 will be made morepronounced than with attachment to the original lower pair.

1. A seat back core comprising a moulded plastics sheet bowed forwardlyin vertical section and with fixing points on the rear side near top andbottom for attachment to a rigid seat member, the back being moreresistant to bending over its upper part than its lower part.
 2. A seatback core as claimed in claim 1, wherein the sheet has side wingsinclined forwardly from narrow zones of weakness within the boundary ofthe sheet, symmetrically disposed either side of a vertical centre lineand generally parallel thereto.
 3. A seat back core as claimed in claim2, wherein the zones of weakness are formed by closed end slots.
 4. Aseat back core as claimed in claim 3, wherein the wings and the centralportion of the core between the slots are connected by bridges acrossthe slots.
 5. A seat back core as claimed in claim 4, wherein thebridges are parts of transverse ribs integrally moulded on the rear sideof the sheet.
 6. A seat back core as claimed in any one of claims 2 to5, wherein the wings are divided into generally horizontal sections eachcapable of limited flexure with respect to the or each adjacent section.7. A seat back core as claimed in claim 6, wherein the division betweenwing sections is by slots extending from the edge of the sheet to theadjacent zone of weakness.
 8. A seat back core as claimed in claim 6,wherein the division between wing section is by expandable membranesintegrally moulded with the sheet and extending from the edge of thesheet to the adjacent zone of weakness.
 9. A seat back core as claimedin any one of claims 2 to 8, wherein the top edge portion of the core,beyond the zones of weakness, is divided into side-by-side sections eachcapable of limited flexure with respect to the or each adjacent section.10. A seat back core as claimed in claim 9, wherein the division betweentop edge portion sections is by generally vertical slots extending downfrom the top edge of the core.
 11. A seat back core as claimed in claim9, wherein the division between top edge portion sections is bygenerally vertical, narrow, integrally moulded expandable membranes. 12.A seat back core as claimed in any preceding claim, wherein thedifferential resistance to bending is caused by further ribs extendingsubstantially vertically between transverse ribs in the upper part ofsaid central zone.
 13. A seat back core as claimed in any one of claims1 to 11, wherein the differential resistance to bending is caused bylocally reducing the thickness of the sheet by transverse grooves and/orscored lines across the lower part of the said central zone.